In recent years, the use of communication systems having wireless mobile communication units which communicate using an optical or radio link with a hardwired network, such as a local area network (LAN), has become quite widespread. Retail stores and warehouses, for example, may use such systems to track inventory and replenish stock. Employees may enter inventory information using a hand held or portable communication unit which can be carried through the store or warehouse. In manufacturing facilities, such systems are useful for tracking parts, completed products and defects. In a medical environment, these systems can reduce the time needed to fill out forms and eliminate inaccuracies by allowing medical personnel to transmit data directly from a mobile communication unit carried by the medical personnel.
A conventional communication system generally includes a number of fixed base stations (i.e., access points) interconnected by a cable medium to form a hardwired backbone network. The network medium may be a twisted pair cable, shielded coaxial cable or fiber optic lines, for example. Each base station has a service area or cell surrounding the base station within which it has the ability to transmit and to receive relatively error-free data from a mobile communication unit within the area. In many instances, the cell is not circular because physical objects within the cell may partially block data signals creating "dead spots" within the area surrounding the base station. Also, machinery located in the vicinity of the base station may generate excessive noise levels that degrade the quality of transmissions between the base stations and the mobile communication units.
In such a network, a mobile communication unit must initially register itself with a base station and then attempt to begin a session with a host computer whereby the host allows communication to occur between itself and the particular mobile communication unit. More particularly, when a mobile communication unit is powered up, it "registers" with a base station. However, as the location of this mobile communication unit changes, the mobile communication unit may register with another base station, thereby resulting in a deregistration with the previous base station. Furthermore, deregistration will sometimes occur if there is no communication between the mobile communication unit and its corresponding base station within a predetermined period of time. Thus, in such communication systems, mobile communication units register and deregister frequently as the mobile communication units are moved about.
As mentioned above, each mobile communication unit within the communication system must also begin and maintain a session with the host computer (or other device which provides application or information based services) once it has registered with a base station. A session is typically only initiated once at start up by each mobile communication unit and is active unit such time as the mobile communication unit ends the session regardless of the number of registrations and deregistrations which may have taken place with respect to base stations during this period. Each mobile communication unit within the communication system has a respective identification code (ID), which allows the host computer or other device on the backbone handling session requests to recognize and distinguish each mobile communication unit. Occasionally, however, an error will occur where the host computer receives a request for a new session whereby the ID associated with the new session request is the same as an ID for an already established session. Similarly, the same type of error could also occur with respect to the mobile communication unit registering with the base stations. The error may be the result of an improperly programmed mobile communication unit wherein the ID was duplicated as a result of the same mobile communication unit accidently re-attempting to begin a new session with the host computer, or may be the result of the ID of the mobile communication unit being corrupted during transmission to the base station or host computer, for example.
This type of error may result in the original mobile communication unit being dumped from the communication system or cause the communication system to lock-up. As a result, data integrity of the original mobile communication unit to host computer session may be lost as a result of the original mobile communication unit being dumped. Furthermore, if the duplicate ID error causes the communication system to lock-up, data integrity of all mobile communication unit to host computer sessions within the communication system may be jeopardized. Accordingly, there is a strong need in the art for a duplicate device ID detection system which overcomes the aforementioned problems associated with a mobile communication unit accessing a communication system with an apparent duplicate ID. In particular, there is a strong need in the art for a system that detects and rejects a mobile communication unit which is attempting to register to a communication system (i.e., with a session request or base station registration process) with a duplicate ID so that a mobile communication unit already registered to the communication system is not deregistered or dumped, and/or the communication system does not lock-up.